1. Field of the invention
The present invention relates to a steering apparatus adapted to support a steering shaft so that a tilt can be adjusted and, more particularly, to a steering apparatus constituted to absorb energy of a secondary crash which is applied to the steering shaft at the time of a vehicle crash, utilizing a guiding portion for tilt adjustment.
2. Description of Related Art
A vehicle is steered by transmitting rotation caused by an operation of a steering wheel disposed in a driver""s room to a steering mechanism disposed outside the driver""s room for turning tire wheels for steering (the front wheels, in general). The steering wheel is mounted at an upper end portion of a steering shaft which is supported in the driver""s room so as to be rotatable about an axis so that a driver can operate the steering wheel.
The steering shaft is rotatably supported in a cylindrical column housing. The steering shaft and the column housing are supported in a tilted orientation with the upper end portion, at which the steering wheel is mounted, leaning backwards. The steering shaft is extended to the exterior of the driver""s room via an intermediate transmittance shaft such as a universal joint or the like, and is connected to the steering mechanism. The steering mechanism has a movement transforming unit, such as a rack-and-pinion, a ball thread or the like, allowing rotation of the steering wheel transmitted via the steering shaft and the intermediate transmittance shaft to the steering mechanism to be transformed into movement for turning the tire wheels via the movement transforming unit.
Some of such steering apparatuses of late years have a constitution with which a position of the steering wheel at an upper end of the steering shaft can be adjusted for realizing driver""s comfortable steering operation. In general, a position of the steering wheel is adjusted with a combination of tilt adjustment for adjusting a tilt angle of the steering shaft along with the a column housing and telescopic adjustment for extending and contracting a middle portion of the steering shaft and the column housing.
Moreover, many of steering apparatuses of late years comprise an energy absorbing mechanism for absorbing energy of the crash, for reducing damage to the driver who has made a crash (a secondary crash) into the steering wheel by the action of inertia to the front at the time of the crash of the vehicle. In general, the energy absorbing mechanism is provided with an elastic portion at a middle portion of the steering shaft and the column housing, which portion is elastic in an axial direction under suitable resistance. Energy of the secondary crash is absorbed in virtue of sliding resistance which is generated while the elastic portion is contracted by action force caused by the secondary crash.
However, in a steering apparatus for a vehicle with a small space at the front portion of the driver""s seat, such as a buss, a truck, a monospace car or the like, the steering shaft has to be supported with a large tilt angle with regard to a floor. In such a state, a direction of force, which is applied to the steering wheel at an upper end of the steering shaft at the time of the secondary crash, scarcely accords with an axial direction of the steering shaft. With a steering apparatus of this kind, the above energy absorption utilizing contraction of the steering shaft and the column housing is difficult to be realized. Consequently, for a conventional steering apparatus used in a vehicle of this kind, an energy absorbing mechanism is employed which absorbs energy of a secondary crash utilizing leaning of the steering shaft in a direction in which the tilt angle increases.
FIGS. 1A and 1B are schematic representations showing a constitution of a steering apparatus comprising an energy absorbing mechanism utilizing an increase of a tilt angle. A steering shaft 1 is rotatably supported in a cylindrical column housing 2, and is mounted to a tilting bracket 4, which is fixed to and supported by a part of a driver""s room, via a column bracket 3 fastened to a middle portion of said column housing 2.
To an upper end portion of the steering shaft 1 which is projected from an upper portion of the column housing 2, a steering wheel 10 is fixed. A lower end portion of the steering shaft 1 which is projected from a lower portion of the column housing 2 is connected via a universal joint 11 and an intermediate shaft 12 to a steering mechanism which is not shown in the figures. Rotation caused by an operation of the steering wheel 10 for steering is transmitted to the steering mechanism via the steering shaft 1, the universal joint 11 and the intermediate shaft 12. The intermediate shaft 12, which is constructed by engaging an inner shaft 12a having a deformed cross section into an outer tube 12b of the same shape, is a telescopic shaft which can be extended and contracted in an axial direction by sliding the inner shaft 12a in and out of the outer tube 12b and can be rotated in one body at a suitable elastic position.
The column bracket 3 having a box-shaped cross section is integrally fastened to an exterior face of the column housing 2. The column housing 2 comprises a pair of upper and lower telescoping apertures 30 and 31 which extend in an axial direction of the column housing 2. The tilting bracket 4 has a cross section which is substantially in the shape of xe2x80x9cUxe2x80x9d with an open portion of both side walls placed downward. The column bracket 3, which is fitted between both side walls of the tilting bracket 4, is mounted with a locking bolt 20 and a guiding bolt 21 which respectively run through the telescoping apertures 30 and 31.
At a side wall of the tilting bracket 4 a tilting aperture 40 is formed which is curved in an arc shape with a through portion of the guiding bolt 21 at a lower position as a center of the arc. The locking bolt 20 at an upper position runs through an intersecting portion where a tilting aperture 40 and a telescoping aperture 30 intersects, and is fastened to said position. At an upper portion of the tilting aperture 40 a guiding aperture 41 is formed to have a curved form in an extension to the tilting aperture 40. At a boundary portion between the guiding aperture 41 and the tilting aperture 40 a stopper 5 is mounted. The stopper 5 which is configured as a tube with a diameter slightly larger than a width of the guiding aperture 41 is fitted at the boundary portion between the guiding aperture 41 and the tilting aperture 40 via a bush 50 made of resin, and is provided transversely between both side walls of the tilting bracket 4.
In a steering apparatus constituted as above, the above tilt adjustment and the telescopic adjustment are performed in a state where the locking bolt 20 is unfastened. The column bracket 3 can move with regard to the tilting bracket 4 fixed to a carbody by sliding the locking bolt 20 and the guiding bolt 21 along the upper and lower telescoping apertures 30 and 31. Telescopic adjustment for displacing the column housing 2 and the steering shaft 1 in an axial direction is caused by the movement of the column bracket 3. This adjustment is achieved by extension and contraction of the intermediate shaft 12 constituted as a telescopic shaft.
Moreover, the column bracket 3 can be oscillated about an axis of the guiding bolt 21 with regard to the tilting bracket 4 fixed to a carbody, by sliding the locking bolt 20 along the tilting aperture 40. Tilt adjustment for adjusting a tilt angle of the column housing 2 and the steering shaft 1 is achieved by the oscillation of the column bracket 3. The steering shaft 1 and the column housing 2 thus can be oscillated about an axis of a connecting portion of the steering shaft 1 and the universal joint 11, and extension and contraction of the intermediate shaft 12 change the tilted orientation.
FIG. 1A shows a state of a steering apparatus having a medium tilt angle, and FIG. 1B shows a state of a steering apparatus having a largest tilt angle. The tilt adjustment is achieved within the limits of an angle from a lower end of the tilting aperture 40 to a position where the stopper 5 is provided.
After performing telescopic adjustment and tilt adjustment as described above, the locking bolt 20 is fastened. By fastening the locking bolt 20, the column bracket 3 is supported between both side walls of the tilting bracket 4. In a state where the steering shaft 1 and the column housing 2 are thus fixed so as to be unmovable, steering is achieved by operating the steering wheel 10 mounted to an upper end of the steering shaft 1.
When a vehicle makes a crash during a steering operation and a driver makes a secondary crash against the steering wheel 10 at an upper end of the steering shaft 1 by the action of inertia caused by the crash, the column housing 2 and the steering shaft 1 are pushed in a direction in which a tilt angle increases, by the action of force applied in a direction which is indicated with the arrows relieved in white in FIGS. 1A and 1B. The column bracket 3 to which the force is applied moves along the tilting aperture 40 until the column bracket 3 crashes into the stopper 5. The stopper 5 into which the column bracket 3 crashes slides into the guiding aperture 41 arranged in an extension to the tilting aperture 40 with searing and destroying the bush 50 made of resin, and keeps sliding with deformation of the stopper 5 until the stopper 5 comes to an end portion.
In the above operation, energy of the secondary crash is successively absorbed by sliding resistance between the column bracket 3 and the tilting bracket 4 caused by movement of the column bracket 3 which is fixed with the locking bolt 20, by energy used for shearing and destroying the bush 50, and by sliding resistance between the guiding aperture 41 and the stopper 5. As a result, action force which is applied to the driver who crashes into the steering wheel 10 is weakened, and driver""s damage can be reduced.
However, in a conventional steering apparatus constituted as above, the above-mentioned absorbability of secondary crash energy is influenced by a state of a crash of the column bracket 3 and the stopper 5. Consequently, there arises a problem that damage can not be reduced as preferably as expected when the column bracket 3 and the stopper 5 crash in an improper manner. FIGS. 2A and 2B show representations for illustrating a state of a crash of the column bracket 3 and the stopper 5, showing a cross section along a direction in which the tilting aperture 40 and the guiding aperture 41 are extended.
The column bracket 3 is configured as a member with a box-shaped cross section, supported between both side walls of the tilting bracket 4 having a cross section which is substantially in the shape of xe2x80x9cUxe2x80x9d. A flat upper face of the column bracket 3 faces the stopper 5 which is provided transversely between the both side walls. When a driver makes a secondary crash against the steering wheel, the column bracket 3 moves in a direction which is indicated with the arrows relieved in white in FIGS. 2A and 2B until the column bracket 3 crashes into the stopper 5. FIG. 2A shows a normal state of a crash and FIG. 2B shows an abnormal state of a crash.
As shown in FIG. 2A, when a whole upper face of the column bracket 3 crashes into the stopper 5 in a substantially even manner with regard to the total length of the stopper 5, force components F0 and F0 (F0≅F/2) with substantially half magnitude of an impact force F applied to a whole crashed portion of the column bracket 3 are respectively applied to bushes 50, 50 which support both sides of the stopper 5. As a result, the bushes 50, 50 on both sides of the stopper 5 are destroyed substantially simultaneously. The stopper 5 slides into the guiding apertures 41, 41 on both sides of the tilting bracket 4, and sliding resistance is generated between the stopper 5 and the guiding apertures 41, 41. Required energy absorption is thus achieved in a normal state of a crash.
On the other hand, for example, when the column bracket 3 moves in a state where the bracket 3 is tilted between the side walls of the tilting bracket 4 before crashing into the stopper 5 and a part of the column bracket 3 crashes into the stopper 5 locally as shown in FIG. 2B, the impact force F is concentrated on this crashed portion. To a bush 50 at a position nearer to the crashed position, which is one of bushes 50, 50 on both sides of the stopper 5, a large force component F1 is applied, while to a bush 50 at a position farther from the crashed position, which is the other of the bushes 50, 50, a small force component F2 is applied. After the former bush 50 is destroyed, the stopper 5 slides into the guiding apertures 41, 41 in a state where the stopper 5 is tilted with a destroyed side thereof placed ahead.
The column bracket 3 which has slid into the guiding apertures 41, 41 comes to a sliding end without enough amount of energy of the secondary crash being absorbed, since a guiding aperture 41 on one side is under small sliding resistance. Consequently, it may occur that a large impact force is applied to the driver when the column bracket 3 comes to the sliding end. Moreover, when the stopper 5 is tilted on a large scale, the stopper 5 is hindered from sliding after sliding into the guiding aperture 41. In such a case, it is possible that energy is not absorbed during a slide of the stopper 5 and a large impact force is applied to the driver.
In a conventional steering apparatus, as mentioned above, it is required that a normal state of a crash as shown in FIG. 2A is always realized, for gaining required absorbability of secondary crash energy. To realize a normal state of a crash, high accuracy is demanded in shaping related parts such as the tilting bracket 4 including the tilting apertures 40 and the guiding apertures 41, the column bracket 3, the stopper 5 and the like. As a result, there arises a problem in that production costs of the steering apparatus increase.
The present invention has been made with the aim of solving the above problems, and an object of the invention is to provide a steering apparatus, with which energy of a secondary crash can always be absorbed under a proper condition utilizing leaning of the steering shaft in a direction in which a tilt angle increases, while high accuracy is not demanded in shaping related parts.
In a steering apparatus according to the present invention, a column bracket provided at the middle of a cylindrical column housing for supporting the steering shaft so as to be rotatable is supported between both side walls of a tilting bracket fixed to a part of a vehicle, so as to be displaceable along tilting apertures which are formed respectively at the side walls of the tilting bracket. Consequently, a tilt angle of the steering shaft can be adjusted. Moreover, the steering apparatus comprises guiding apertures arranged in an extension to the tilting apertures beyond an adjustable region of a tilt angle, and a stopper which is provided transversely between the side walls at boundary portions between the tilting apertures and the guiding apertures. The stopper, which is pressured by the column bracket by the action of energy of a secondary crash applied to the steering shaft at the time of a crash of the vehicle, slides along the guiding apertures. Furthermore, the steering apparatus comprises a contact projection or contact projections provided on the stopper and/or on the column bracket in such a manner that a projection on one member is projected toward the other member from a substantially center portion between both side walls of the tilting bracket.
When the column bracket slides between side walls of the tilting bracket at the time of occurrence of the secondary crash and crashes into the stopper in a state where the tilt angle comes to a limitation of adjustment, the crash occurs at the contact projection provided at a center portion in a width direction of the stopper and/or the column bracket. Action force generated at this crashed portion is applied to both end portions of the stopper which are supported on the both side walls of the tilting bracket, as substantially equal force components. Consequently, the stopper slides along the guiding apertures arranged in an extension to the tilting apertures under an even condition for each of the guiding apertures on both sides, and thus energy of the secondary crash can be reliably absorbed. In the steering apparatus according to the present invention, high accuracy is not demanded in shaping related parts.
Moreover, the steering apparatus according to the present invention is constructed in such a manner that each side of the stopper is supported at a boundary portion between the tilting aperture and the guiding aperture via a supporting bush made of resin. Consequently, a slide of the stopper along the guiding apertures with the crash of the column bracket is achieved in a stable manner via the supporting bushes made of resin, and energy of the secondary crash can be absorbed further reliably.
Furthermore, in the steering apparatus according to the present invention, the boundary portion between the tilting aperture and the guiding aperture, where the stopper is mounted, is formed to have a greater width than other portions. Since the supporting bushes on both sides of the stopper are accommodated in the boundary portions formed to have a greater width than other portions, the stopper can avoid being moved by a slight crash of the column bracket during tilt adjustment. Moreover, energy of the secondary crash can be reliably absorbed.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.